The present invention relates generally to nickel-cadmium storage batteries, and more particularly, to a method for removing excess electrolyte from such storage batteries during their manufacturing process.
Nickel-cadmium (Ni/Cd) batteries are an important energy storage device for small communication satellites, for example. In the manufacture of these batteries, and in particular hermetically sealed batteries, it is important that just the right amount of liquid electrolyte be added to each battery cell. Overfilling a cell, even by a small amount, interferes with the rapid recombination of gaseous oxygen, evolved during charging cycles, with the cadmium metal at the negative electrode. Such recombination is essential if the build-up of excessive gas pressure within the cell and permanent "bulge out" damage are to be avoided. Underfilling the cell can also result in reduced battery service life because of an insufficient amount of electrolyte in the separate between the anode and cathode of cell, a condition known as separator "dry out."
Typical present day nickel-cadmium batteries have separators made from either nylon or polypropylene felt material. In the manufacturing process for such batteries, overfilling of a cell, either by a mistake in estimating the amount of electrolyte required or by a manufacturing accident, can be corrected merely by inverting the battery and then charging it in this position, whereupon, under the force of gravity, the excess electrolyte liquid flows out through the fluid fill tube.
Recently, an improved design for these batteries has been introduced. In these "super" nickel-cadmium batteries, the felt separators have been replaced by a zirconia separator material. However, it has been found that because of the stronger capillary action exhibited by the zirconia separators, the above-mentioned technique used for correcting the overfilling problem has not been effective.
It is therefore an objective of the present invention to provide a technique and method which enables the removal of an excess electrolyte from nickel-cadmium and super nickel-cadmium battery cells.